There are currently labeling machines available wherein endless conveyor chains are arranged to move wiper assemblies along a container supporting conveyor for pressing labels against the sides of containers moving along with the container conveyor. The label assemblies approach the container around a sprocket at one end and leave it about a sprocket at the other end and the only pressure exerted is from the rubber pads of the wiper assemblies. The unidirectional movement of the wiper assemblies provides for high speed operation without undue vibration in contrast to the reciprocal type wiper assemblies, however, part of the travel between sprockets is used up to get the wipers into engagement with the containers and a part is used up to move them away so that they do not remain in engagement with the containers long enough to insure permanent sticking of the labels. Engagement of the wiper pads with the containers for a greater length of time could be provided for by employing larger sprockets and larger chains, however, this is objectionable because the ratio of the number of whiper assemblies engaged with the containers at any one time is high with respect to the number of wiper assemblies mounted on the chains and because the larger sprockets results in high speed around the ends which develops destructive centrifugal forces. The purpose of this invention is to provide a structure wherein the unidirectional movement of a conveyor chain type of wiper assembly supports and its advantage of high speed operation can be availed of with relatively small sprockets and short chains without sacrificing the length of the time that the wiper pads are in active compressive engagement with the containers; a structure which is designed to enable making adjustments of the wiper assemblies at opposite sides of the container conveyor and to maintain uninterrupted drive from a common source and to automatically maintain tautness in the conveyor chains.